1. Field of the Invention
The present invention relates to a light-emitting diode in which a light-emitting chip is sealed by a transparent sealing member and to a vehicular lamp and more particularly to a structure of the sealing member of a light-emitting diode and to a vehicular lamp that uses such a light-emitting diode.
2. Description of the Related Art
In recent years, light-emitting diodes are used more often in vehicular lamps as its light source.
Light-emitting diodes are generally comprised of, as disclosed in Japanese Patent Application Laid-Open (Kokai) No. 2001-283616, a light-emitting chip, which is disposed on a predetermined optical axis, and a transparent sealing member, which seals the front side of the light-emitting chip on the optical axis. The front face of the sealing member has a substantially spherical surface.
Japanese Patent Application Laid-Open (Kokai) No. 2002-94129 discloses a light-emitting diode in which the rear face is a reflective surface so that the light emitted from the light-emitting chip is used more efficiently.
The feature of the above-described conventional light-emitting diodes is that the luminance of the emitted light rapidly decreases according to the increase in the divergence angle from the optical axis, which is manifested in the form of a luminance distribution. This, however, causes problems that such a light-emitting diode cannot radiate light with sufficient luminance in an oblique direction while the light-emitting diode radiates light with sufficient luminance in the forward direction.
When such light-emitting diodes as described above are used as a light source of a vehicular lamp, several problems occur.
Most of vehicular lamps have a mechanism that controls the light emitted from the light source by a lens disposed in front of the light source so as to create a light distribution pattern that exhibits balanced luminance distribution. However, when a light-emitting diode is used as a light source, such a lens arrangement cannot sufficiently mitigate the sharp luminance distribution of the light-emitting diode. As a result, such a lamp radiates light with an extremely great intensity to the front of the lamp (which is so-called pin-point illumination), and this problem cannot be solved.
In addition, for most of the vehicular lamps, there is a need to make the size of the lens of a lamp as large as possible in order to secure a sufficient light-emitting area. In this case, the light emitted from the light-emitting diode reaches the perimeter of the lens at a significantly wide incident angle, and this reduces the lens efficiency. As a result, a further problem occurs that the light directed from the perimeter of the lens is significantly low in intensity as compared to the light directed from the center portion of the lens.